1. Field of the Invention
The present invention relates to a process for treating and regenerating waste solutions from photographic treatments. Particularly, the present invention relates to a process for treating waste solutions containing ferricyanide and/or ferrocyanide ions from photographic treatments.
2. Description of the Prior Art
In some cases, a bleaching step is included in treatments for photographic materials. Bleaching is a treatment whereby materials such as silver formed by development are returned to ionic form using an oxidizing agent, and is included in treatments for silver halide color photosensitive materials and silver dye bleaching photosensitive materials and reduction treatments for photographic materials used for printing.
In general, ferricyanides such as potassium ferricyanide are used as the oxidizing agent in bleaching solutions. In some cases, potassium bichromate, iron chelates, quinones and copper salts are used as the oxidizing agent instead of the ferricyanides. However, the ferricyanides are the most preferred bleaching agents from the view point of oxidizing power, ease of bleaching and their stability. However, faults encountered in using bleaching solutions containing ferricyanides are that the deteriorated bleaching solution must be replaced and ferricyanide ions discharged by overflowing during the treatment or by rinsing after bleaching, and ferrocyanide ions resulting from reduced ferricyanide ions, produce cyano compounds by photochemical oxidation (see "Behavior of Cyano Compounds in Water Ponds" Gidrokhim. Materialy 37, 133 - 43 (1964) written by Yu. Yu. Lur'c and V. A. Panova, and "Toxicity of Ferro- and Ferricyanide Solutions to Fish and Determination of the Cause of Mortality" Trans. Am. Fish Soc. 78, 192 (1948) written by George Edgar and Morris Lipschuetz).
Such cyano compounds have a strong toxicity and if introduced into the environment exhibit a very harmful pollutant effect.
In the past, quite often waste solutions containing ferricyanide and/or ferrocyanide ions have been discharged without any treatment.
To attempt to obviate the pollutant effects of cyano compounds on the environment, it has been suggested to reuse overflow bleaching solutions and deteriorated bleaching solutions which contain ferricyanide and/or ferrocyanide ions by regenerating such solutions. In order to reuse a bleaching solution by regenerating, it has been suggested to use persulfates (U.S. Pat. No. 2,944,895), ozone (French Pat. No. 2,015,461), iodine (British Pat. No. 1,229,077) and peracetic acid (French Pat. No. 2,005,207),etc.
However, even if regeneration is carried out using such processes, the ferricyanide ions and/or ferrocyanide ions are still carried in a washing bath, which is followed by a rinsing. Since the amount of the ferricyanide ions and/or ferrocyanide ions in the rinsing water is very small, the above mentioned process for regenerating cannot economically be utilized at all. Since the cyano compounds formed from the ferricyanide and ferrocyanide ions by photochemical decomposition have a very strong toxicity, it is necessary to remove the cyano compounds even though they are present in a small amount in the rinsing water. Ferricyanide and ferrocyanide ions at such low concentrations can nonetheless be removed by the formation of precipitates by reacting them with iron salts, by electrodialysis, by reverse osmosis or by a combustion or pyrolysis method, etc.
The formation of precipitates by reaction with iron salts utilizes the reaction between ferricyanide and ferrocyanide ions and iron ions to form Prussian blue. However, this method has the fault that it requires a long time for the sedimentation and large sedimentation apparatus because the particles of Prussian blue formed are very fine. Particularly in the case of a low ion concentration and a large quantity of water, such as with rinsing water, the precipitation method is difficult to carry out, and requires a large scale equipment.
Though the electrodialysis method and the reverse osmosis method are effective for treating solutions of a low concentration such as rinsing or washing water, they have the fault that the necessary equipment is expensive. This fault is especially encountered in treating solutions having a large quantity of water such as rinsing water, i.e., the cost of the equipment becomes very high because large apparatus is required. Further, the cost of operation is high because of the large amounts of electricity consumed.
The combustion method comprises evaporating and decomposing the waste solution at a high temperature by means of a heavy oil burner or the like. A similar method involves pyrolyzing wherein chemicals such as sodium hypochlorite are added to the waste solution followed by decomposition at high temperature. In the case of applying these methods to waste solutions from photographic treatments containing ferricyanide and/or ferrocyanide ions, very large heat sources are necessary because of the large quantity of water involved. Further, the ferricyanide ions will damage a combustion furnace because of their high oxidation ability, both a serious fault of the combustion or pyrolysis method.
On the other hand, with methods other than the combustion or pyrolysis method, the treatment of waste liquor results in a sedimentary residue or liquid waste. These products must be treated to make them harmless, but this is very difficult. If the ferricyanide and/or ferrocyanide ions contained in a photographic waste liquor could be recovered and reused as, e.g., a bleaching solution, this would be the best solution to this problem because ferricyanide and/or ferrocyanide ions would not be discharged at all.